Apparatus for deriving diffractive rays by diffraction gratings

ABSTRACT

Apparatus for deriving diffractive rays by diffraction gratings which enables light measurement to be effected with high accuracy in addition to the feasibility of making the whole apparatus in a compact size. These features of the apparatus are obtained by the provision of a photoelectric element on the rear side of an index grating at a position in which it faces a movable scale grating with a small distance from this latter grating.

United States Patent 1191 Kimura Jan. 8, 1974 APPARATUS FOR DERIVING3,154,688 10/1964 Shepherd 250/237 0 DIFFRACTIVE RAYS BY DIFFRACTION2,964,636 l2/l960 Cary 1. 250/216 X GRATINGS 3,668,404 6/1972 Lehovec250/237 G 3,569,997 3/1971 Lehovec 250/237 G [75] Inventor: KatsuhikoKimura, Tokyo, Japan [73] Assignee: Olympus Optical Co., Ltd., PrimaryExaminer walter Stolwein Tokyo'to Japan Attorney-John W. Malley et al.[22] Filed: July 11, 1972 21 A p]. No.: 270,688

[57] ABSTRACT [30] Foreign Application Priority Data Apparatus forderiving diffractive rays by diffraction July 17, 1971 Japan..;.,46/73584 grating enables measurement to be effected with high accuracyin addition to the feasibility [52] U.S. Cl 250/237 G, 356/169, 2 50/234f making the whole apparatus in a compact size Illl. l These features ofthe apparatus are obtain d the Field of Search 250/237 G, 216, 231 R,provision of a photoelectric element on the rear side 250/234; 356/169170 of an index grating at a position in which it faces a movable scalegrating with a small distance from this [56] References Cited lattergrating.

UNITED STATES PATENTS 3,1 14,046 12/1963 Cabaniss et 'a1 250/237 G 1Claim, 3 Drawing Figures Pmmmm 81974 3.784.833

PRmR ART APPARATUS FOR DERIVING DIFFRACTIIVE RAYS BY DIFFRACTIONGRATINGS BACKGROUND OF THE INVENTION 1. Field of the invention Thepresent invention pertains to an apparatus for deriving diffractive raysby diffraction gratings.

2. Description of the prior art It is known that precise and exactlength or angle can be measured by either observing the positionalchanges of the moire-image interference fringes caused by the movementof one of the two separate transparent gratings or by metering the lightrays representing such positional changes. In performing such ameasurement, there arises no problem in case these two gratings arespaced apart from each other at a relatively great distance. However, incase this distance is decreased to the order of the wavelength of lightrays, there develops the phenomenon of diffraction of rays. Thisphenomenon, in turn, gives rise to a considerable lowering contrast ofthe moire-image interference fringes, making it difficult to take theexact measurement under such condition. In order to intensify thecontrast of moireimage interference fringes, therefore, it has been thepractice to use an arrangement as shown in FIG. 1. More specifically,the light rays coming from a light source 1 impinge onto a scale grating3 through a collimator lens 2. The light rays emitting from an indexgrating 4 are received by a photoelectric element 7 via a projectionlens and a slit 6.

With the foregoing arrangement of the apparatus, however, it has beendifficult to produce this apparatus as a whole in a compact size and ata low cost.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is anillustration showing the arrangement of the essential parts of a knownapparatus for deriving diffractive rays by diffraction gratings.

FIG. 2 is an illustration showing an example of the arrangement of theessential parts of the apparatus for deriving diffractive rays bydiffraction gratings which embodies the present invention.

FIG. 3 is an illustration showing another example of the arrangementaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, reference numeral 1represents a light source which is installed at a fixed position.Numeral 2 represents a collimator lens for rendering the light rays fromthe light source 1 to parallel rays. Numeral 3 represents a scalegrating which is comprised of a grating member 3a made with a replicaofa synthetic resin and a thin planar glass sheet 3b securely attachedto the rear side of said grating member 3a to serve as the base of thisgrating member. This scale grating 3 is arranged so that it is able tomake a precise and exact movement in the direction of the arrow by meansof a device not shown. Numeral 4 represents an index grating which iscomprised of a grating member 4a made with a replica of a syntheticresin and a thin planar glass sheet 4b securely attached to the rearside of said grating member 4a to serve as the base of this gratingmember. This index grating 4 is arranged at a fixed position in such away as to face said scale grating 3 at a small distance therefrom.Numeral 7 represents a photoelectric element such as SPD and havingterminals 7a and 7b and being fixed directly to the rear side of theindex grating 4 by an appropriate fixing means 8.

The apparatus according to the present invention is of the foregoingarrangement. The light rays coming from the light source 1 pass throughthe collimator lens 2 and impinge onto the scale grating 3. The lightrays which are thus transmitted through the scale grating 3 will thenimpinge onto the index grating 4. Then, the light rays emitting fromthis index grating 4 will reach the light-receiving surface of thephotoelectric element 7. As such, when the scale grating 3 is moved inthe direction of the arrow, the moire-image interference fringes whichare produced on the light-receiving surface of this photoelectricelement 7 will move accordingly. Thus, it is possible to derive theamount of move ment of the scale grating 3 as the change in the electricamount such as current or voltage. It should be understood, however,that by arranging the apparatus so that the scale grating 3 is fixed andthat the index grating 4 together with the photoelectric element 7 ismoved in the direction of the arrow, there is obtained a result equal tothat described above.

FIG. 3 shows another example of the apparatus embodying the presentinvention. In this example, there are provided as the light source aplurality of luminous diodes 9 which are arranged behind the scalegrating 3 along therewith. Also, a plurality of photoelectric elements 7are arranged on the rear surface of the index grating 4. According tothis arrangement of the apparatus shown in FIG. 3, it is possible toproduce the apparatus in a more compact size as compared with the oneshown in FIG. 2.

I claim:

1. An apparatus for deriving diffractive rays by diffraction gratings,comprising a movable scale grating arranged in the foreground of a lightsource, said source including a plurality of luminous diodes arrangedalong said scale grating immediately adjacent thereto, an index gratingfixed at a small distance from said scale grating and facing the lattergrating, and a plurality of photoelectric elements arranged immediatelybehind said index grating and integrally fixed to the rear side thereof,said apparatus being arranged to be operative so that the light rayscoming from said light source impinge directly onto said scale gratingand that the light rays emitting from said index grating are received bysaid photoelectric elements.

1. An apparatus for deriving diffractive rays by diffraction gratings,comprising a movable scale grating arranged in the foreground of a lightsource, said source including a plurality of luminous diodes arrangedalong said scale grating immediately adjacent thereto, an index gratingfixed at a small distance from said scale grating and facing the lattergrating, and a plurality of photoelectric elements arranged immediatelybehind said index grating and integrally fixed to the rear side thereof,said apparatus being arranged to be operative so that the light rayscoming from said light source impinge directly onto said scale gratingand that the light rays emitting from said index grating are received bysaid photoelectric elements.